A fuel cell has been proposed as a clean, efficient and environmentally responsible power source for various applications. In particular, individual fuel cells can be stacked together in series to form a fuel cell stack capable of supplying a quantity of electricity sufficient to power an electric vehicle. Accordingly, the fuel cell has been identified as a potential alternative for a traditional internal-combustion engine used in modern vehicles.
A common type of fuel cell is known as a proton exchange membrane (PEM) fuel cell. The PEM fuel cell includes three basic components: a cathode, an anode and an electrolyte membrane. The cathode and anode typically include a finely divided catalyst, such as platinum, supported on carbon particles and mixed with an ionomer. The electrolyte membrane is sandwiched between the cathode and the anode to form a membrane-electrode-assembly (MEA). The MEA is disposed between porous diffusion media (DM). The DM facilitates a delivery of gaseous reactants, typically hydrogen and oxygen from air, to an active region defined by the MEA for an electrochemical fuel cell reaction. Nonconductive gaskets and seals electrically insulate the various components of the fuel cell.
When the MEA and the DM are laminated together as a unit, for example, with other components such as gaskets and the like, the assembly is called a unitized electrode assembly (UEA). The UEA is disposed between fuel cell plates, which act as current collectors for the fuel cell. The UEA components disposed between the fuel cell plates are typically called “softgoods”. The fuel cell plate has a feed region that uniformly distributes the gaseous reactants to and between the fuel cells of the fuel cell stack. The feed region may have a broad span that facilitates a joining of the fuel cell plates, e.g., by welding, and a shifting of flows between different elevations within the jointed plates. The feed region includes supply ports that distribute the gaseous reactants from a supply manifold to the active region of the fuel cell via a flow field formed in the fuel cell plate. The feed region also includes exhaust ports that distribute the residual gaseous reactants and products from the flow field to an exhaust manifold.
Lower performing cell (LPC) conditions, fuel cell instability, and degradation due to reactant starvation or non-uniformity of reactant flow have been observed when at least one of the softgood components is forced into the port features in a phenomenon known as “softgood intrusion.” Softgood intrusion occurs when there is a pressure differential between a cathode side and an anode side of the barrier film sufficient to deflect the softgoods into the port features. The pressure differential often occurs during normal operation of the fuel cell.
It is known in the art to support the softgoods in the feed region and inhibit softgood intrusion by adding a metal shim or foil. Metal shims have been used to sandwich and sufficiently support the softgoods against deflection. However, the use of metal shims is undesirable since the shims must have a strength and thickness that resists deflection of the softgoods under the pressure differential. The metal shim must also be sufficiently bonded to the softgoods to inhibit a separation therefrom over repeated fuel cell operation. The employment of metal shims undesirably adds to a complexity and cost of the fuel cell.
There is a continuing need for a fuel cell that provides sufficient softgood support without the use of metal shims. Desirably, the fuel cell minimizes softgood intrusion and militates against low performing cell conditions, fuel cell instability, and fuel cell degradation due to reactant starvation or non-uniformity of reactant flow to the fuel cell.